1. 3D-printing of thin films with stencil masks
There is a growing demand for micro and nanofabrication technologies, to enable device miniaturization and multi-functionality integration [1] [2], especially for complex oxides, which broad spectrum of optical, electronic, magnetic, etc. properties offers tremendous application opportunities [3] [4] [5]. These materials are usually physically hard and chemically inert which make them difficult to structure by standard technologies including mechanical machining or chemical etching steps, e.g., standard top-down approach, including ion beam structuring, electro beam writing or photo-lithography.
Direct patterned deposition through the use of masks is then a very promising alternative: by maintaining the mask in close contact with the substrate, the structures of the mask are replicated onto the substrate by depositing through its opening. This approach has the advantages of being a single step fabrication method, further allowing parallel processing of a full wafer [6] [7]. To optimize the mask concept, stencil masks, consisting of small thin membranes in which apertures are drilled and which are hold within larger wafer holes, have been developed, allowing pattern resolution down to 50 nm [8].
FIG. 1 presents some of the major problems associated with state of the art technology, which principally are [9] [10]:                a) The blurring, which is a widening of the deposited pattern dimension compared to the stencil aperture size, due to the existing gap between the stencil and the substrate. It generally has two origins: first, a purely geometrical factor and secondly, the formation of an additional halo around the deposit due to diffusion of active species between the mask and substrate at the aperture edges which decompose. Compliant membranes have been developed to reduce efficiently the blurring effect [11] maintaining substrate and mask in close contact, independently of both parallelism. However in the case of the present invention, reduction of the substrate-mask gap is not an absolute priority, as it is exploited in the process.        b) The clogging, which is the aperture size reduction with time due to material deposition on the side walls of the apertures. It is particularly problematic when deposited thickness is of the same order or higher than the aperture size in the case of nano-stencils. It changes the mask opening dimension and the apparent stencil thickness.                    A solution as been proposed with the incorporation of micro-heaters in the stencil [12] for physical deposition process. This is no solution for a chemical deposition technique in which reactive species decompose due to thermal heating, and it does not work with non volatile species. Another developed strategy to prevent clogging is to functionalize the stencil with mono-layers that prevent deposition on it [13]. This solution however works poorly in the present invention, the coating being fragile when heated or exposed to organometallic precursor flows under vacuum conditions.                        c) The membrane stability: stencils usually consist of 50-500 nm thick Si or SiN membranes, which are very fragile. They are in particular sensitive to the stress induced by material deposition on top of them and thermal effects. Stabilized and corrugated membrane developments enable to reduce problems associated with this effect [14; 15].        
FIG. 1 describes deviation from ideal case of the deposition process using stencil mask. In the idealized case (image a), a punctual source of reactive species contributing to the deposit (SE), is situated at a large distance, h, from the mask (SM), of infinitely small thickness, that is in close contact to the substrate (SU), with a small gap g close to 0, but non null. The mask aperture of dimension dO is replicated with same dimensions leading to deposition (D) on the substrate.
In the real case, the emission source has a non-zero dimension (dE). The gap g is not zero, so due to geometric factors, the aperture of dimension dO results in a deposit of dimension dGB due to geometrical factors. Additionally, some reactive species may diffuse in the gap between mask and substrate and realize an additional halo deposit of dimension dGH around the main deposit. The enlargement of the deposit dimension with respect to mask aperture dimension is called blurring (image b).
In addition, deposition may take place on the mask top and side (image c), leading to clogging, due a deposit Dm that affects the aperture dimension (reduced from dO to dOm) and mask thickness (increased from t to tm).
The deposition of material on the mask, and more specifically on the stencil membranes within the mask, is the main problem that the present invention proposes to solve, to ensure better stencil mask re-usability and longer mask life time.
Stencil deposition has mainly been used for metal deposition by evaporation, but stencil principle can also be applied to material etching [16] [17] or material local modification, for instance by ion implantation [9]). Oxides have also been deposited selectively through stencil masks, by room temperature PLD [18], high temperature PLD [19] [20], non reactive magnetron sputtering [21] and MBE [22]. The use of such a physical vapour deposition (PVD) technique with stencil masks is referred to as stencil lithography, and today, first devices based on such techniques have been demonstrated [7] [23] [24].
Considering chemical vapour deposition techniques, Chemical Beam Epitaxy (CBE) and related techniques (Metalorganic Molecular Beam Epitaxy (MOMBE), Gas Source Molecular Beam Epitaxy (GSME)) have been demonstrated for more than 25 years of being highly compatible with the use of shadow mask to realize selective deposition [25] [26]. Micrometric III-V structures have been deposited and their application to integrated laser/waveguide applications [27] have for instance been shown. Compared to the PVD methods previously quoted, Chemical Beam Epitaxy offers the advantage that the chemical reaction responsible of the deposition can be controlled by precursor flow and temperature to induce selective area deposition [28].
2. Tags to Fight Anti-Counterfeiting and Ensure Identification and Traceability
2.1 Description of the Problem
2.1.1—Fighting Anti-Counterfeiting and Tracing Products
Forgery and counterfeiting are problematic that organised societies have had to fight since the very beginning. Everyone is aware of counterfeited products such as luxury goods, e.g. watches, handbags, jewels, softwares, DVDs, CDs, etc., but the plague also extends to new products such as pharmaceuticals or toys, where the problem is no longer only economical, but also impacting people's health or even putting their lives at risk. Today, it is estimated that counterfeit goods are sold worldwide annually for more than $600 billion and that 10% of all sold medicines are counterfeit.
2.1.2—Securing Data and Tracing Information
As our society evolves faster and faster, mainly thanks to a plethora of new emerging technologies, new solutions and services blossom, leading to new needs that could not be anticipated even a few years ago. A main topic in this direction is the emergence of the security related to improved global communication (ICT) facilities. To protect both physical and virtual identities, either at individual or collective levels, new behaviours and organisational rules emerge, demanding fast adaptation to systems of increasing complexity. Among other priorities of ICT, we can mention passwords that are needed to securely connect to everything (cyber-security), starting from close range objects like our PCs, to virtual databases (e-banking, etc.) or social platforms (Facebook, LinkedIn, games, etc. . . ), up to very complex collaborative clouds or networks. Today, as existing solutions are rapidly getting obsolete, more and more elaborated solutions are proposed to protect ourselves from highly invasive and aggressive intrusions coming either from next door neighbours or crossing the planet. The problem is growing to epic proportions with topics such as big/small data and the “internet of things” where a huge mass of information will have to be exchanged in a secure, rapid and efficient way. The societal plague associated with the lack of security of such systems (with identity hacking, frauds, phishing scam, intrusion into privacy etc. . . ) is getting person oriented and carries a huge emotional impact, involving everybody without any discrimination of age, sex and educational level. There is today a strong need to identify in a secure way a really huge number of objects/persons/concepts and no assessed solution is presently at hand.
2.2 Foreseen Solutions for the Problem
2.2.1—Taqs/Etiquettes/Labels Concept and Their Requirements
To fight against anti-counterfeiting, two types of object labels are developed [29, 30]:                “authentication” labels, which confirm in a safe way the nature of the product, the brand logo, etc.        “track and trace” labels which carry additional specific information such as serial number, etc. and allow an object traceability.        
Usually, the technologies used to realize these labels are divided into 3 groups:                “overt technology”: authentication areas on the product are visible, they can be checked by eyes. These include for instance holograms [31], OVDs [32] (optical variable devices, which are marks that change colours depending on the direction they are looked at), watermarks [33] (which are images created by variation of paper thickness), colour or fluorescent ink marks, bar codes, etc. . .        “covert technology”: authentication areas on the product are hidden, they can only be checked with an adapted reader. They include for instance UV sensitive, IR sensitive or thermochromics inks [34, 35], taggants (fluorescent or magnetic nanoparticles, etc. . ),        “machine readable technology” : authentication areas on the product require sophisticated equipment to be identified. These include synthetic ADN marking [36] biological or chemical nanoparticles inclusion, etc . . . They also include sophisticated “Track and Trace technologies” such as radiofrequency identification (RFID) [37] tags and Electronic Product Codes (EPCs).        
Any truly effective modern anti-counterfeit system should display three elements: authentication, identification and track/trace capabilities. For that, the label should fulfil 4 obligations: (1) be difficult to duplicate or forge, (2) have a part easy to identify visually without any special equipment, (3) being difficult to remove from a product, to replace or re-use on another product and (4) have an invisible track and trace fingerprint, machine readable, containing an important amount of information. In the case of remote authentication, a cryptographic solution should also be required to secure the exchanged information.
A further difficulty to overcome for an efficient technology is an economic one [38]: should it provide a product a totally unique, with an irreproducible signature, etc., there is no hope for its development if the tag price is higher than the likely loss of income through counterfeiting.
2.3—State of the Art—Existing Solutions
2.3.1 Solutions for Authentication/Anti-Counterfeiting
Several techniques exist and are used to achieve authentication, security and anti-forgery solutions:                biological or chemical identifiers: isotopes, molecules-ADN, fluorescent, rare earth, nano-structures, chemical composition;        electronic devices: RFID, biometrics, fingerprints, electrical signatures (PKI or DRM);        optical: holograms, security inks, nano pigments, nano-capsules, magnetic nano-particles, polymers micro-tagging, radiography;        mechanical/chemical/laser machining: marks, embossing, lapping, machining, etching, thermal deformation, micro-nano structuring; or        coatings.        
On one hand, naked eye reading is a quite subjective and time consuming solution at large scale and overt technology labels contain a very limited amount of information. On the over hand, covert or machine readable technologies require expensive/poor-mobility readers
With regards to the production techniques, printing methods are the most common. Two different printing approaches are today available, either based on sequential (or serial) printing or based on parallel printing techniques:                the first methods of serial printing usually suffer from low resolution (thus containing low amount of information) or are time consuming and poorly cost efficient if higher resolution (with micro or nano dots resolution) is targeted (like for Plixel Printing). The time required to print a highly resolved etiquette/tag/label is such that this method will never be suitable to address efficiently huge mass production of high security/high information density. This is an intrinsic limit of such serial printing technologies. With regards to the high-resolution printers, when they get affordable and readily available on the market, the security will just get obsolete rapidly;        the second methods of parallel printing (printing simultaneously all the surface) could allow cost effective mass production and with high resolution. However, the matrix production cost is usually very high and all the codes are identical, allowing neither flexibility nor variations on the tag (which is actually where the traceability and possibly enhanced security lays). Again, if the core technology is cracked (the matrix is duplicated), all the security associated with this solution is gone.        
It is believed that a cost-effective and secure mass production that is not getting rapidly obsolete because of forgery is not available in prior art, with standard printing methods as demonstrated by constantly evolving adoption of novel solutions for banknotes and similar objects.
For these reasons, additional security for anti-counterfeiting or anti-forgery is provided through inks (main player is SICPA). Main examples are on banknotes or other secured documents. Usually, there are two scales of effects: macro-scale with a printed message (names, pictures, serial numbers, . . . ) where information is given by some order in the structure and random micro-nano scale effects that serve as an anti-forgery mechanism for the ink itself. In the first case, a pattern can be seen by naked eye, but does not provide any security mechanism. In the second case, random structures, that can be identified only through the use of a special dedicated reader, do not usually contain any information, but provide security. Among the additives in inks, we can quote fluorescent (KR20110126885) or other optical effects induced by micro or nano particles (KR20110006836, JP2010237448, EP1882176, CN1940013, DE102005019980, US2005112360, GB1536192), embedded/dispersed/printed into markers or tags/etiquettes, (with companies such as TraceLess or Microtrace) etc. . . Printing methods with special inks make an intensive use of such additives, the inks providing optical functionalities or other functionalities like electrical conductivity (CN1869134, CN1917097, WO2008053702) to the printed pattern. We can list, among others, NanoIMG (US2010050901) with embedded micro and nanostructures in an invisible unique code, Nanum with its Magnetic Ink Character Recognition (MICR) inkjet ink technology, or DNA barcodes from UATEC University in Portugal or Tracetag that exploits specific chemical reactivity of embedded molecules in the barcode. When the ink secret composition is cracked, however, all the documents based on the technology can be forged. Another drawback is related to recycling of such tags as mentioned in previous work (JPS62206695, JP2009276564) that very often contain rare or toxic elements.
As an alternative, we can quote ink-less printing methods such as laser writing or marking on bulk materials like ceramics (GB2284404) or laser modifying the surface properties of materials to achieve optical effects. Lasers are mainly proposed to achieve a marking effect without containing any security out of the possible complex substrate material composition and its patterning. Enhanced effects with a laser for improved security, also make use of additional polymer films (CN101143958) or multilayer films (JP2006007592) that are modified by laser irradiation in a very difficult to counterfeit way. Nevertheless, again these techniques suffer from most of the same intrinsic limits of printing methods with inks.
Hot embossing or other mechanical/thermal deformation techniques (such as proposed by Tesa or Scribos) of a tag or directly of the object itself is also extensively used. Several holograms, consisting in engraved/embedded micro or nanostructures with optical effects on micro-regions, can be combined offering an appreciated resistance to forgery. Among others we can mention those developed by Hologram Industry based on interference micro lithography or digital holography, which are also used in a wide number of applications.
Further solutions are based on identifying already existing defects in the bulk material matrix/texture of a tag or object itself. This is the solution proposed by Proof-tag or Ingenia Technology with a laser surface identification technique. These methods are, however, very sensitive to the degradation of the object and identification of patterns can be quite time consuming. Furthermore, they require complex and time-consuming reader solutions.
Patterned thin films are also been proposed (CN1547180) using for example TiO2 composites or patterned polymer films (TW201225026) using wetting and optical properties effect combination. Several other inventions are disclosed for polymers or easily etchable or machined materials such as resins (US2008248266, JPH04118690), but with limited lifetime due to poor mechanical and chemical stability of the materials.
Iridescent thin films have also already been proposed (JP2005085094), but only to achieve an optical effect as a function of the viewing angle. Another invention (KR20040045270) discloses different materials to achieve monochromatic wavelength contrast due to different optical thicknesses. Materials with different refractive indexes are provided to achieve such an effect, leading either to limited effects or to very expensive assembly manufacturing.
Finally, multi-region or multi-functional tags have also been proposed (CN201025567, CN201020901), consisting in a vertical assembly of different solutions. These solutions are however quite expensive and complex to realize.
With regards to the idea of combining traceability and security, a solution called “TAG” exploits two components (an anti-counterfeiting tag and a QR code) that are combined in a single solution. On one hand, such solution claims that the copper wires cannot be replicated, but the set-up is relatively simple and for sure cannot guarantee a huge number of different combinations. On the other hand, the QR contains a very limited amount of information (black and white dots of low resolution).
Thin film vacuum deposition technologies have been recognized for a long time as efficient technologies to create security or anti-counterfeiting labels [39].
Among these, we may quote:                luminescent quantum dots [40];        overt optical label combined with magnetic covert label [41];        covert plasmonic security labels based on Ag nanowire structures and their polarization dependent surface-enhanced Raman scattering (SERS) imaging [42];        over identification by Surface-Enhanced Raman Scattering [43];        nano-optics and near field optics [44];        invisible marks: patterns on LiF crystals by EUV [45] [46];        photonique nanostructures [47];        use of multifunctional material [48];        the use of non toxic or dangerous materials is highly preferable [49];        
Concerning the reading tag technologies, we may quote:                angle dispersive X-ray diffraction (X-ray detection in packaging (patent No U.S. Pat. No. 7,756,248 from Panalytical B. V., 2009);        Raman scattering (Erasable taggant distribution channel validation method and system, patent U.S. Pat. No. 7,875,457 B2 from Axsun Technologies, 2004);        wettability [50];2.3.2 Solutions for Identification/Traceability        
Two standard general techniques are used:                bar codes: a barcode is a machine-readable optical label that contains information about the item to which it is attached. They replace an alpha numeric code by a geometric pattern code.        
Referring to FIG. 9, bar codes include linear barcodes Lmade up of lines and spaces of various widths that create specific patterns, such as for instance the UPC, Universal Product Code) or 2D bar codes (composed of 2D geometrical patterns, such as the trademark QR-codes (Quick response code) or the Data matrix code, which is free of use) .
The advantage of these codes are easy and cheap printers/readers with a huge availability to the average population with readers as simple as a Smartphone. These solutions can provide identification of 1 object out a group of a million units up to roughly one billion units. Higher pattern resolution is required to increase information density and address larger groups of objects. Furthermore, no security is tied to these codes that can thus be easily copied and reproduced or moved to different objects.
The bar codes ease of reading is also their main weakness as anyone can forge or counterfeit them. Furthermore, such marks contain only very limited amount of information and when large numbers of objects are to be tracked (over 1 billion), the system rapidly gets to its limits. One solution is to further increase dot resolution or to add colour (JPS62206695, CN2448723), but this still yields intrinsic limits to security and anti-forgery issues.                RFID (radio frequency identification)        
RFID tags contain electronically stored information that is read by wireless non contact readers. They are either powered , behaving as local power source and operate up to few hundred meters, or non powered, emitting either microwaves or ultra-high frequency radio waves when exposed to magnetic fields (by electromagnetic induction).
RFID Tags [51] or electronic tags (WO2012053716, US2008149731) are nowadays employed in a very broad range of applications, to track goods and products, objects, such as baggage, accesses, for instance to public transportation, people, for instance in hospitals, animals, etc. . . These RFID tags offer high reliability without contact reading method, but readers and codes themselves are getting quite expensive and with a poor mobility. The advantage of such tags is remote reading without mechanical or visual contact. However, these tags are quite expensive (15 cts for passive tags, 25 dollars for active tags [52]) and usually require bulky readers or energy supply. Furthermore, a huge quantity of tags (above 1'000) within a reader will lead to confusion and misreading. As a further disadvantage we can also quote that RFID, or other purely electronic systems, are usually providing poor security as tags can be moved from one product to another easily. They also contain polluting elements such as chrome in appreciable quantities. Finally, being a remote reading process, tracking of people wearing such tags on their products is a main limit to this technology as it disregards any privacy policy. Companies involved in such a field are, for example, Secure RF or Tagsys.
Another solution is the Contact Memory Botton, electronic component used by the US army and developed by the company TITANOX Industrie.
Further electronics popular solutions range from biometric identification (fingerprints, eye pattern, face feature recognition, etc. . .). However, these solutions cannot be applied to objects.
2.3.2. Data Security
The next societal evolution in ICT will be related to traceability and connection of objects with their relative information exchanged in a secured way and this constitutes the field of the “Internet of Things” or “Internet of Everything”. There, huge quantities of data (Big Data or Small Data) related or emitted by practically any kind of objects will require a protocol merging the security and traceability covering both the PCs and the objects interconnected as well as an encrypted information to provide remote authentication.
It appears obvious today that constantly innovating solutions have to be found to secure Big Data [53, 54, 55, 56, 57, 58]. Some solutions are proposed in [59, 60, 61], including again RFID.
When we are speaking about security today, the first thing that comes to the mind, very often even before house or streets security, is Cyber-security and passwords to protect our virtual life. Several solutions are today available, but most are based on software-based solutions to encrypt information that can, however, be remotely hacked. Password-based systems furthermore have the weakness than when the password is cracked unlimited access is guaranteed. Furthermore, the over-increasing number of required passwords leads to poorly safe methodology to generate and store such passwords at individual level. More secure systems, involving hardware for PW generation, rely on additional manual time consuming endless password checks that are a real hurdle to the end-user and cannot manage a huge number of secured transactions in a timely manner. Actually, today this is the only secured procedure to avoid automatic cracking of codes by computers.